Hydrazine hydrate,
Sodium cyanoborohydride,
Methanol,
Water,
Trifluoroacetic acid.

To a solution of di-(Ac-Phe-(e-keto)aminopimelate(OLi)-OLi) pentahydrate (61.4mg, 141umol) in HPLC grade CH₃OH (2mL) was added hydrazine hydrate (70uL, 72.1mg, 1.44mmol). The solution was acidified to pH 5.0 by the careful addition of CF₃CO₂H and after 30min NaCNBH₃ (89.4mg, 1.42mmol) was added. The reaction was stirred at RT overnight, then acidified by the addition of conc. aq. HCl. Solvent was removed in vacuo and the solid residue dissolved in deionised water (1mL). The solution was applied to the H⁺ form of a column of Dowex AG50 WX-8 cation exchange resin (2mL bed volume) and eluted with deionised water until the washings were neutral. The desired product was eluted with 1N NH₃ in deionised water. Removal of solvent afforded the product as a glassy semi-solid (52.1mg, 132.2umol, 93.8%).

Addition of water to the methanolic solution of the ketone can aid solubility and does not decrease the yield. The important aspect of the reaction is to get the pH of the solution to ca 5.5 to 5.0 by the careful addition of TFA - use of a microsyringe to add microlitre amounts works well. This procedure also works for reductive amination - in this case ammonium acetate is a convenient ammonia source. This reaction was performed on a small scale conveniently in a 5mL Wheaton vial.

¹H(300MHz; D₂O) 7.25 (5H, m, Ph), 4.60 (1H, m, CH), 4.15 (1H, m, CH), 3.55 (1H, m, CH), 3.20 (1H, m, phe CH), 2.95 (1H, m, phe CH), 2.20 (1H, m, AP CH), 1.95 (3H, s, CH₃), 1.90-1.20 (5H, m, AP + CH₂ + CH); m/z (ES⁺, H₂O/D₂O) 394 (M)⁺ 5%, 395 (M-H+D)+ 80%, 396 (M-2H+2D)+ 75%, 397 (M-3H+3D)+ 65%, 398 (M-4H+4D)+ 33%, 399 (M-5H+5D)+ 8%.

"Synthesis and in vitro enzyme activity of peptide derivatives of bacterial cell wall biosynthesis inhibitors." R. J. Cox, H. Jenkins, J. A. Schouten, R. A. Stentiford and K. J. Wareing, J. Chem. Soc., Perkin Trans. 1, 2000, 2023-2036.

"Inhibitors of N-Succinyl Diaminopimelic Acid Aminotransferase (DAP-AT) : A Novel Class of Antimicrobial Compounds." Russell J. Cox, James A. Schouten, Rosie A. Stentiford and Katrina J. Wareing, Bio. Med. Chem. Lett., 1998, 8, 945-950. "Synthesis and Evaluation of Novel Substrates and Inhibitors of N-Succinyl-LL-Diaminopimelate Aminotransferase (DAP-AT) From E. coli." R. J. Cox, W. A. Sherwin, L. Lam and J. C. Vederas, J. Am. Chem. Soc. 1996, 118(32), 7449-7460.